This is a fantastic puzzle! It's not too easy, nor is it too hard to solve. It comes from the mind of a brilliant Japanese puzzle inventor called Osanori Yamamoto, whose Bisect Cube puzzle was one of the first things I uploaded to Thingiverse. Not only are all his designs very clever puzzles, but many of them are also ideally suited to 3D printing as they require no additional support. The puzzle consists of one ring shaped piece and four identical T pieces. These must be assembled with the Ts arranged in a mirrored pairing as shown in the photo. The design was downloaded from the Puzzle Will be Played website at http://www.puzzlewillbeplayed.com/643Ring/FourMirrorOne/As usual, I have created the STL files with a small bevel (to remove sharp edges which can snag during movement) and a 0.1 mm offset (to give the pieces room to move). Each unit cube is 8 mm on a side but feel free to scale the puzzle up or down in size as you wish. Do bear in mind however that the fit will get looser as the puzzle gets larger, and tighter if you print a smaller copy. Print one of the ring pieces (S1) in one colour and four of the T pieces (S2) in a different colour. I prefer a medium infill and 0.2 mm layer height to ensure a nice smooth top surface.